const TAG_NAME = '[A-Za-z][A-Za-z0-9-]*';
const ATTRIBUTE_NAME = '[a-zA-Z_:][a-zA-Z0-9:._-]*';
const UNQUOTED_VALUE = '[^"\'=<>`\\x00-\\x20]+';

const SINGLE_QUOTED_VALUE = "'[^']*'";
const DOUBLE_QUOTED_VALUE = '"[^"]*"';

const ATTRIBUTE_VALUE = `(?:${UNQUOTED_VALUE}|${SINGLE_QUOTED_VALUE}|${DOUBLE_QUOTED_VALUE})`;
const ATTRIBUTE_VALUE_SPEC = `${'(?:\\s*=\\s*'}${ATTRIBUTE_VALUE})`;

export const ATTRIBUTE = `${'(?:\\s+'}${ATTRIBUTE_NAME}${ATTRIBUTE_VALUE_SPEC}?)`;

export const OPEN_TAG = `<(${TAG_NAME})(${ATTRIBUTE})*\\s*/?>`;
export const CLOSE_TAG = `</(${TAG_NAME})\\s*[>]`;

export const HTML_TAG = `(?:${OPEN_TAG}|${CLOSE_TAG})`;

export const reHTMLTag = new RegExp(`^${HTML_TAG}`, 'i');
export const reBR = /<br\s*\/*>/i;
export const reHTMLComment = /<! ---->|<!--(?:-?[^>-])(?:-?[^-])*-->/;

export const ALTERNATIVE_TAG_FOR_BR = '</p><p>';

export const DEFAULT_TEXT_NOT_START_OR_END_WITH_SPACE = 'a';